Source and Pathway Sensitivity in Troposphere-to-Stratosphere Transport: An Adjoint-Based Approach

大气对流层上层/平流层下层区域(8-20公里)的臭氧是地球辐射收支的一个重要组成部分，因此在决定气候方面具有作用。众所周知，这一地区的臭氧对卤化物种的化学消耗也很敏感。自从《蒙特利尔议定书》在生效以来，氯氟碳(CFCs)等长寿命卤化物种的排放量一直在下降。因此，人们的兴趣集中在化学寿命较短的替代物种以及海洋排放的天然卤化物种上。这些物种中有许多被称为“极短寿命物种”(VSLS)，它们的化学寿命为6个月或更短。相对较短的寿命意味着，随后排放到平流层下部的化学物质的比例是不确定的，在那里它可能会导致臭氧消耗。特别是，由于与当地天气模式相关的不同输送影响，到达较低平流层的比例可能对排放化学品的地理位置高度敏感。目前的建议旨在量化不同地理排放地点对向平流层下层输送极小武器的相对重要性。此外，将以“敏感度图”的形式计算在不同地点排放的示例性VSLS的臭氧消耗潜力。敏感度图将使政策制定者能够直接评估如果特定地表地点排放特定的VSLS可能发生的臭氧消耗量。提出了一种通过求解化学输运方程的“伴随”来计算灵敏度图的新方法。除了有效地解决VSLS问题外，新方法还具有应用于大气化学和传输中的许多不同问题的潜力。因此，该提案的次要目标是在英国大气科学界内促进联合方法。

Ozone in the upper troposphere / lower stratosphere region of the atmosphere (8-20km) is an important component in Earth's radiative budget, and therefore has a role in determining climate. Ozone in this region is also known to be sensitive to chemical depletion by halogenated species. Since the Montreal protocol came in to force in 1989, emissions of long-lived halogenated species such as chloro-fluoro carbons (CFCs) have been in decline. Consequently, interest has focussed on replacement species with shorter chemical lifetimes, as well as natural halogenated species emitted from the oceans. Many of these species, known as `very short-lived species' (VSLS), have chemical lifetimes of six months or less. The relatively short lifetime means that the proportion of an emitted chemical that subsequently reaches the lower stratosphere, where it may cause ozone depletion, is uncertain. In particular, the proportion reaching the lower stratosphere may be highly sensitive to the geographical location where the chemical is emitted, due to differing transport effects associated with local weather patterns. The current proposal aims to quantify the relative importance of different geographical emission locations for the transport of VSLS to the lower stratosphere. Further, the ozone depletion potential of example VSLS emitted at different locations will be calculated in the form of a `sensitivity map'. The sensitivity maps will allow policymakers to straightforwardly assess the amount of ozone depletion that is likely to occur if a particular VSLS is emitted from a particular surface site. A novel approach to calculate the sensitivity maps, based on solving the `adjoint' to the chemistry-transport equation, is proposed. In addition to efficiently solving the VSLS problem the new method has the potential to be applied to many different problems in atmospheric chemistry and transport. A secondary aim of the proposal is therefore to promote the adjoint approach within the UK atmospheric science community.